Sir Andrew Green is Chairman of MigrationwatchUK. He was formerly HM Ambassador to Syria and Saudi Arabia.

Ministers have perfected a patter when talking about immigration. “We’re sorry – we’ve made mistakes, but we’re now getting it under control with our new, tough, Australian-style Points Based System”, they say. Last week, in his first speech on immigration in two years, Gordon Brown trumpeted the merits of the Points Based System (PBS) for immigration and citizenship. He claimed that "together they constitute a fundamental reform of a decade's old system – a reform founded on the British values of personal responsibility and civic duty."

Sadly, this “reform” fails entirely to address the central challenge we face: by 2029, official forecasts show that our population will hit – and then exceed – 70 million. 70% of this growth will be due to immigration. Put another way, in 25 years we will need to build seven cities the size of Birmingham to house new migrants. To avoid that, migration needs to be reduced dramatically – down from the 237,000 net migration in 2007, down also from the 150,000 net migration forecast for 2008, to around 50,000 – as the graph below shows (click it to enlarge). Bear in mind that even this cut would mean our population will rise by nearly 4 million.

The Points Based System fails completely to meet this challenge. Like a fake Rolex, look at it closely and it is fatally flawed. Its coverage is very limited, it is very complex, there is enormous scope for abuse and there is every risk that it will collapse in chaos. If it does, our ability to remove those who have fooled the system is pathetically weak. So, if our challenge is to stop the population hitting 70 million, the PBS is not fit for purpose.

First, coverage. Phil Woolas, the Immigration Minister, claimed on Newsnight recently that the PBS covered just under half of immigrants to Britain if students were included. Wrong. This claim is based on a passenger survey of those who declare that they intend to stay for longer than a year. Obviously, those who intend to overstay are not going to participate in the survey. The more relevant measure is the number of visas issued every year which is nearly 2 million. Only 20% of those granted visas come for the purposes of work or study and so are covered by the Points Based System.

Consequently, claims that the PBS will stop the population hitting 70 million are misleading. The Government trumpet recent falls in immigration as proof that the PBS is working: but 70,000 (76%) of the fall was due to a fall in net migration from the EU which is not subject to the PBS and over which the government has no control. More crucially, the Government’s own assessment is that, if the Points Based System had been fully operational in 2008, it would have reduced immigration by only 20,000 to 217,000. But – to repeat the point above – immigration will need to be reduced to 50,000 if the population is not to hit 70 million.

Next, scope for abuse. The new system has effectively taken Immigration Officers out of the equation. Nobody seems to have noticed that it has also effectively contracted out the critical phase in the issue of visas for work and study. Once granted a licence, an employer or an educational institution can issue a certificate which is the key to obtaining a visa. Clearly, those bodies have every interest in bringing people to this country and very little interest (or capability) to ensure their departure – even if they wished to. The Government have blandly announced that they have struck off 1,800 educational institutions from the 4,000 recognised under the previous system. What has been going on these last twelve years?

Third, complexity. Gordon Brown also told us how much simpler the new system is than that which he inherited in 1997. Not quite. The website of the UK Border Agency illustrates the complexities. There are nearly 800 pages of forms and guidance – a bonanza for immigration lawyers and a burden for industry. There are potentially 26,000 job titles and thousands of sponsors. There could well be half a million applications a year. On past form, the Home Office are most unlikely to have the staff and resources necessary to check the authenticity of the sponsors. The pressure from industry and academia will be to reduce waiting times and backlogs. Already, there are cries from the Home Affairs Committee of the House of Commons for a system of appeals. It could well be only a matter of time before we find that the Home Office are simply going through the motions for the sake of appearances, as we have so often seen in the past.

If, or rather when, the system starts to go wrong, there will be no redress. Our capability to remove overstayers is pathetically small. The government inflate the figures for removals by including those turned away at the border and allowing multiple counting of those turned away in Calais. The true figure is about a thousand a month compared to the two million visas issued every year.

What of the Conservatives? They have said that they will accept the Points Based System subject to modification. The first modification must be to restore the role of immigration officers. However, the crucial step is that recommended by the Economic Affairs Committee of the House of Lords in April 2008 – namely a broad target range for net immigration around which the necessary measures can be built. David Cameron's response at a recent press conference that he wished to see immigration brought down to the levels of the early 1990s (about 40 to 50 thousand) is the right approach. Given the widespread and growing public concern about the scale of immigration, it cannot happen soon enough.